Connected: An Internet Encyclopedia
RFC 1772 - 3.2 Global Nature of BGP

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### 3.2 Global Nature of BGP

At a global level, BGP is used to distribute routing information among multiple Autonomous Systems. The information flows can be represented as follows:

                        +-------+         +-------+
                  BGP   |  BGP  |   BGP   |  BGP  |   BGP
               ---------+       +---------+       +---------
                        |  IGP  |         |  IGP  |
                        +-------+         +-------+

                        <-AS A-->         <--AS B->

This diagram points out that, while BGP alone carries information between AS's, both BGP and an IGP may carry information across an AS. Ensuring consistency of routing information between BGP and an IGP within an AS is a significant issue and is discussed at length later in Appendix A.

Next: 3.3 BGP Neighbor Relationships

Connected: An Internet Encyclopedia
RFC 1772 - 3.2 Global Nature of BGP